Monday, August 29, 2011

We're preparing for a move. This will absolutely disrupt an already shaky path of progress. How long? Who knows. Onward and upward, I'm fully looking forward to upgrading space. In the meantime, I'm going to endeavor to ramp up my posting here, so as to not lose sight. I think this is going to turn into more small posts and a few one liners.

Threaded tape on the Otari again, pictured here is a destructive alignment issue. Machine appears to be keeping speed (the first tape I played appears to have been recorded on a machine with SERIOUS issues, dishing up a heap of red herrings).

Once I have the tape path free of obstructions I plan on buying a proper calibration tape.

Friday, August 26, 2011

This sort of thing bothers me.

I recently cracked the case on a console radio to be met with a musty wave of air and chalky white controls in similar condition. Internet searches for "plastic mold", "chalky white film knob" and similar are largely useless. Though after wading a bit I found this thread:

Which offers up some solutions to the problem. I think I'll avoid the dishwasher one, as, if this is indeed a byproduct of early plastic decomposition I doubt I'll want it anywhere near my food. Just a quick share, mainly secure the thread without another half hour of aimless searching for myself (while avoiding the creation of yet another topic specific forum bookmark in my browser).

Saturday, August 20, 2011

More broken speakers pushing into the pipeline.

I was cleaning out the van today, and happened across this driver I have been meaning to take a picture of. A Jensen C15-L hailing from the 20th week in 1970 (near as I can figure) that spent some time loaded in the folded W horns of my PA system.

I recall the performance of this driver as being particularly good in the bin, capable of pushing an authoritative bass note that numbed the skull. As it happened, I was supplying sound for an outdoor party several years back, and did not have appropriate limiting on the low end.

I was, of course, well aware that low end in an outdoor environment is essentially lost in relation to the very steep enclosure reinforcement we're used to hearing, so I didn't push the levels of the lows. Sadly, it didn't matter. A beat box vocalist laid down serious LF excursion with the plosive burst bass notes, and I had nothing high passing subsonics, basically paving the way to the condition we see here.

I believe once the over excursion separated the cone from the voice coil, further current passing through the speaker welded everything together. It's looking like a 2 inch coil, and I expect to see BBQ country once I crack the shell on it, which may be a while, considering...

Sunday, August 07, 2011

Let's cut some stuff open. Here's a pair of blown Sunn Magna 158A 15 inch transducers; the later 200 watt variety, not to be confused with the square magnet CTS 80 watt drivers. Neither are operable, and the likelihood of a model specific recone kit to surface is practically non-existent.

It would be a shame to let that cast aluminum basket and massive magnet assembly be melted down and reformed into useless junk.

First step is easy, it involved a knife. I did sever the gasket as uniformly as I could prior to digging the cone out, because I can ALWAYS use 15 inch gaskets. For the record, there are two 15 inch folded horns that are awaiting drivers, and four 2x15 cabinets. I expect a slough of recone posts in the future, as time and money allow.

Anyway, back to the 158A. A friend shoulder tapped me to assist in reconing a torn up JBL D130, and it occurred to me that I've got a small collection of JBLs awaiting recone too, and before performing work that I am not 100% familiar with, I may as well work through some of my own before taking on his.

Then, as lateral pondering tends to do, I remembered the Sunn speakers rotting away in storage. It certainly seems reasonable to check fitment of the JBL cone kit with the Sunn basket, worse it can do is not fit before being installed in the frame it was built for. Hopefully in the same era 4 inch voice coils were made more or less the same, 4 inches..

This particular shot isn't inherently clear, it is the nominal measurement of the depth of the coil former from inside edge to spider, an Xmech variable. The D140 recone kit specifies a former height of 0.860 inches, which is very close to what I have here.

I should stress that all of the measurements pictured are pretty rough, pictured are fast and dirty field measurements more for proof of concept than anything else. I have JBL D130, JBL D140 and JBL 2226 up for recone, and each of these will be mocked up on the Sunn 158A basket, and I will certainly opt for the best fit if any actually seem to work in the first place. Make no mistake, I'm not measuring this out to order a kit based on measurements alone.

Internal diameter of coil gap, fairly accurate, though I cannot be certain my pinch point is the widest point in the gap I can be certain the caliper is seated within the gap itself. The caliper is also built out of ferrous material, so magnetism was applicable.

Outer diameter is, however, a total crapshoot. I couldn't physically get the caliper to seat within the gap due to caliper readout chassis, and above disclaimers also apply...

I feel pretty good about this particular measurement though.

Something the recone kit provider does not supply is the cone depth, so I'll have to see if I can dig up this measurement on that dimension at the JBL library at lansingheritage.org, just, you know, to appease my sense of curiosity.

Subtracting this amount naturally. And yes, I might just directly measure the cleaned out basket of the JBL drivers instead of attempting to reverse engineer this cryptic (though very important) dimension. I came up with 2.9440 inches after subtracting one from the other.

The two baskets now sit gutted, masking tape shielding the gap, awaiting some sort of progress. Progress is good, it's probably going to be a bumpy couple months here (relocation is afoot). In the event of success I will indeed link the source of the recone kit I am going to use.